Zostera muelleri is considered conspecific withZ. capricorni, Z. mucronata and Z. novazelandica. This species has been reclassified as Nanozostera (Tomlinson and Posluzny 2001), although here it is retained in the genus Zostera.

Phylogenetic analysis of morphological characters and DNA sequences of samples from a limited number of locations in New Zealand have identified a lack of molecular divergence among Australian and New Zealand Zostera, which were formerly segregated as four distinct species (Z. capricorni, Z. muelleri, Z. mucronata and Z. novazelandica), as well as a lack of reliable morphological characters to separate these four species (Les et al. 2002). Consequently, Les et al. (2002) recommended the taxonomic merger of Australian/ New Zealand Zostera into a single species, Z. capricorni.

Recent molecular genetic and morphological analysis has indicated that Z. capricorni and Z. muelleri should be considered synonymous (Waycott et al. 2004). Jacobs et al. (2006) then suggested the retention of the name Z. muelleri as the original and final species name rather than Z. capricorni.

More comprehensive surveys and phylogenetic analyses maybe required to definitively confirm the existence of a single species for these four species (Turner and Swartz 2006).

Justification:Zoster muelleri is found in Australia, New Zealand and Papua New Guinea. It is threatened locally by coastal development, although throughout its range there are no major declines. This species is widespread in Southern Australia and is listed as Least Concern.

This species is very common. It is primarily a temperate species that extends into the tropics up the east coast of Australia to Papua New Guinea.

There are many locations where there are declines due to coastal development in southern Australia, but there are also locations where it is increasing. Overall, the population is most likely stable or expanding.

Zostera muelleri is a fast growing species and readily colonizes. It rapidly takes over where soft sediments predominate in coastal habitats and is often the dominant species in estuaries and coastal lakes. It shows prolific seed production and there are some annual populations known in New Zealand and south Western Australia.

The leaf width morphology is variable and can sometimes be confused with thin H. uninervus when the leaves are very thin. It is an ecologically important habitat-producing species, providing food and shelter for numerous fish and invertebrate species.

This species may occur in small numbers in permanently open estuaries such as intertidal shoals (Carruthers et al. 2007).

This species is affected by localized threats including coastal industrial development, eutrophication and sedimentation.

In the tropical parts of its range it will be increasingly susceptible to increasing temperatures, as it is less tolerant than tropical species. Climate change may be a threat, but the effects are unknown.

Zostera muelleri was affected by a wasting disease in New Zealand in the 1960s.

There are no specific conservation measures for this species. Given that there is some taxonomic uncertainty associated with this species, more comprehensive surveys and phylogenetic analyses maybe required to definitively confirm the existence of a single species (Turner and Swartz 2006).